EP0094486A1 - Dispositif et méthode pour tester les propriétés conductrices d'un conducteur - Google Patents

Dispositif et méthode pour tester les propriétés conductrices d'un conducteur Download PDF

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Publication number
EP0094486A1
EP0094486A1 EP83102551A EP83102551A EP0094486A1 EP 0094486 A1 EP0094486 A1 EP 0094486A1 EP 83102551 A EP83102551 A EP 83102551A EP 83102551 A EP83102551 A EP 83102551A EP 0094486 A1 EP0094486 A1 EP 0094486A1
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EP
European Patent Office
Prior art keywords
signal
conductor
frequency
test
phase
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Granted
Application number
EP83102551A
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German (de)
English (en)
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EP0094486B1 (fr
Inventor
Thomas Herman Di Stefano
Arnold Halperin
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International Business Machines Corp
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International Business Machines Corp
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/20—Investigating the presence of flaws
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/28—Testing of electronic circuits, e.g. by signal tracer
    • G01R31/2801—Testing of printed circuits, backplanes, motherboards, hybrid circuits or carriers for multichip packages [MCP]
    • G01R31/281—Specific types of tests or tests for a specific type of fault, e.g. thermal mapping, shorts testing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49002—Electrical device making
    • Y10T29/49004—Electrical device making including measuring or testing of device or component part

Definitions

  • This invention relates to apparatus for and method of testing the conductive properties of a conductor.
  • U S specification No. 3,299,351 (Williams) is concerned with the problem of locating a fault in a cable having a metallic sheath covered by a layer of insulating material and buried in a conducting medium (i.e. the ground). Williams applied a composite signal between the metallic sheath and the conducting medium to establish a voltage field in the medium.
  • the composite signal had an average DC current level of zero and comprised a first component having a fundamental frequency and a second component having an even (e.g. second harmonic frequency). Williams then detects the voltage gradient in the voltage field along the cable using two spaced probes and establishes the position of the fault when the voltage gradient reverses.
  • the Applicants are concerned with the problem of detecting current constricting defects (such as cracks, narrow conductors, line breaks, intermittent open, etc) in conducting elements, such as printed circuit lines. Neither the Whitley or the Williams proposals are applicable to this problem nor can the Whitley or Williams apparatus be used to solve the Applicants problem.
  • defects are detected by detecting the second harmonic voltage signal produced by passing a composite AC plus DC test signal through the conductor.
  • the test signal generator is balanced and adjusted to provide a signal which is symmetrical and thus provides little even harmonic distortion.
  • the second harmonic voltages across the conductor result primarily from conductor nonlinearities (incipient faults) and the use of the second harmonic technique provides testing capability for such nonlinearities which are not detectable by ordinary testing techniques.
  • the theory of operation depends upon local changes of resistance caused by ohmic heating in nonlinearities which, while conductive, might be expected to fail early during the normal life of the conductor.
  • the composite alternating current plus direct current test signal passes through the conductive path being tested in an unbalanced wave and, upon encountering a local constriction, causes a small volume of metal in the constriction rapidly to heat and cool in a fashion to generate second harmonic signals in close phase relationship to the unbalanced wave.
  • This temperature change produces a resistance change which varies monotonically with the temperature in response to the AC plus DC current at the frequency of the resistance change.
  • the resistance change produces time varying voltage components at frequencies including the fundamental frequency, second harmonic, third harmonic, fourth harmonic and additional harmonics.
  • the second harmonic signal is the largest signal easily distinguished from the fundamental; it is the second harmonic signal that is amplified and detected.
  • This nonlinearity-generated signal may be several orders of magnitude smaller than very similar signals reflected from a good conductor of relatively great length occurring as a result of resistance heating. There is, however, a phase difference which permits the good conductor generated signals to be filtered out, thus isolating the constriction defect generated signal.
  • a feature of the invention is the use of the second harmonic nonlinearity-generated signal (2f 0 GV) together with phase detection to eliminate the effects of good conductor signal reflections (2f 0 CV).
  • apparatus for testing the conductive properties of a conductor comprising a test signal generator for providing a periodically varying composite test signal comprising a DC current component and an AC current component and for providing a periodically varying comparison signal having the same frequency as the test signal, said composite signal being such that when applied to a conductor comprising a conductive property capable of periodically varying in value at the same frequency as the test signal, a fault signal is produced including a fault component periodically varying at twice the frequency of the test signal; circuit means for applying the test signal to the conductor to be tested; frequency doubling means connected to receive the comparison signal for providing a reference signal having twice the frequency of the comparison signal; first means connected to the circuit means so as to receive the fault signal, for separating the fault component therefrom; phase comparing means connected to receive the reference signal and the fault component for comparing the phase of the two received signal and providing an output signal indicative of the result of the comparison; and means responsive to the output signal for providing an indication of any varying conductive property.
  • a method of testing for varying resistance of a conductor when subject to a varying current comprising generating and applying a composite test signal to the conductor, said signal comprising DC and AC components and having a fundamental frequency; generating a reference signal having twice the fundamental frequency and a predetermined phase relationship with the test signal; deriving a singal from the current flowing in the conductor and selecting from that signal any fault-indicating component having a frequency twice the fundamental frequency; comparing the phase of the fault component and the reference signal; and providing an indication of a detected fault as a result of the comparison.
  • FIG. 1 is a block diagram of the tester of the invention.
  • Probes 1 and 2 connect the circuit on the device 3 under test (which may be a printed circuit board) to a composite test signal tap 4A on test signal generator 4, which comprises oscillator 5 and power amplifier 6, and DC source 7.
  • the test signal from tap 4A is applied via probes 1 and 2 to the appropriate circuit of device 3 which is under test. If the device under test is free of nonlinearity faults there will be no significant generated harmonics. If, however, the device under test contains a nonlinearity (such as a crack which is subject to ohmic heating) there will be a nonlinearity generated signal including harmonics. The second harmonic is most significant.
  • the device under test is connected to f 0 reject filter 8 to reject the test signal fundamental frequency (f 0 ) and, of course, the test signal direct current component.
  • the output of filter 8 is amplified by linear amplifier 9, filtered through a second harmonic band pass filter 10 and amplifier 11, and provided to phase detector 12.
  • Phase detector 12 thus has applied to it, from amplifier 11, the amplified second harmonic generated by the nonlinearity fault of the device under test.
  • phase detector 12 has applied to it a second harmonic signal, from f tap 4B, derived from oscillator 5 of the test signal generator 4.
  • the fundamental frequency is doubled by frequency doubler 14, filtered through band pass filter 15 at 2for and phase shifted by phase shifter 16.
  • the fault signal is phase-sensitive-demodulated and converted to a direct current voltage.
  • This direct current voltage is amplified by logarithmic amplifier 17 to get a wide range of readings.
  • the output of amplifier 17 can be connected to a meter 18 or a go, no-go threshold detector 19 with a defect indicator 20 such as an indicator light, marker or sorting device.
  • a continuity detector 21 and continuity indicator 22 are used.
  • the linear signal amplifier is disabled by amplifier disabling circuit 23 so false readings are not made.
  • the theory of operation depends upon second harmonic signals generated from a local change of resistance caused by ohmic heating at the nonlinearity and the characteristic heating-cooling cycle at the nonlinearity which differs markedly (as to phase) from the characteristic heating-cooling cycle of the conductor along its length. Cooling at the nonlinearity is fast, due to conductive heat transfer to adjacent volumes of cooler metallic conductor, and heating is relatively fast because of conductor constriction, localized higher currents, eddy currents and localized heat buildup causing even higher resistances.
  • the heat cycle is closely related to the phase of the AC signal.
  • Cooling along the length of the good conductive element is relatively slow, and heat buildup to a maximum occurs due to the heat insulating properties of the insulation and the fact that incremental volumes of the metallic conductor have no adjacent volumes of cooler metallic conductor.
  • the heat cycle is not closely related to the phase of the AC signal, differing by approximately 90 0.
  • a current source consisting of an alternating current with a direct current flows through a constricted conductor
  • the small volume of metal rapidly heats and cools asymmetrically on the half wave enhanced by the DC bias. This produces a resistance change which varies monotonically with the temperature change.
  • the current flowing through this changing resistance produces a voltage response which has nonlinear components including even harmonics of the current drive.
  • the second harmonic generated signal from a good conducting line could be much greater in amplitude than the signal from a defect.
  • some characteristic differences should be recognized.
  • the temperature rise and fall due to the drive signal follows the power waveform closely, because of a short thermal time constant, producing resistance changes and second harmonic voltage changes of a particular phase.
  • the temperature rises and falls due to the drive signal are integrated, due to long thermal time constants, and the resulting second harmonic generated voltage is phase-shifted with respect to the signal from a defect.
  • phase detector If the phase detector is aligned so that the second harmonic from a long conducting line is nulled out, only defect signals will be detected. It should be noted that an optimum drive frequency should be used so that the amplitude of the signal from a good conductor is small and yet should have a large phase difference from the signal due to a defect.
  • the optimum frequency of operation is one that is high enough to provide a small signal from the conducting line and low enough so that the defect signal is not reduced or phase-shifted.
  • a is a constant.
  • ⁇ is equal to K times the power dissipated at the construction. K depends on the physical dimensions of the constriction and other components producing the thermal time constant. Dimensions of K are °C/watt.
  • the sine wave source is balanced in such a way as to minimize the second harmonic signal when no defect is present in the conductor under test. It is essential to the operation of this second harmonic technique that the source current contain both a DC and a pure sine wave AC component. Without the DC component, a nonlinearly conductive defect would produce a voltage signal containing only odd harmonics.
  • the third harmonic component is not detected, as is done in the prior art, because the third harmonic produced by the defect would be mixed with the signal resulting from third harmonic impurity in the source current.
  • the source impurity would then mask the presence of any nonlinear conductivity due to conductor defect.
  • a sine wave current source will exhibit large odd harmonic impurities (including the third) that are due to cross over distortion, saturation, etc.,. that cannot be eliminated by carefully balancing the circuitry.
  • the theory of operation is described for a model current constriction as shown in FIGS. 2 and 2B.
  • the approximation is made that the constriction cools by conduction of heat out to the main body of the conductor.
  • conductor 24 has a resistive constriction 25.
  • Local heating at constriction 25 produces a positive second harmonic current/ voltage response different from that of a linear ohmic device as shown in Fig. 2B.
  • a conductor 26 may have a tunnelling constriction 27, as shown in FIG. 3A.
  • This tunnelling constriction produces a negative second harmonic current/voltage response as shown in FIG. 3B.
  • the voltage produced across the constriction is composed of a DC component, a fundamental component, the second harmonic component which we are particularly interested in, and higher frequency components.
  • FIG . 4 shows in stylized fashion a conductor 28 having a constriction 29 which may be a resistive constriction as shown or may be a tunnelling constriction.
  • FIG. 5 shows current i, resistance R and voltage V on a time scale with all harmonics included in the R and V waveforms.
  • FIG. 6 shows the waveforms for i, R and V for the case in which the drive current i is a pure sine wave with no DC component.
  • the odd harmonics are removed from the R waveform and the even harmonics removed from the V waveform.
  • FIG. 7 is a graph of log V 2f over log f, showing a representative reference line at 1.0 KHz.
  • the voltage of the conductor diminishes on a different response curve than does the voltage across the defect.
  • the second harmonic voltage generated by the defect is near a maximum difference from the second harmonic voltage generated by the conductor.
  • F IG. 8 is a diagram illustrating the phase difference of the second harmonic signals related respectively to the conductor and to the defect.
  • the defect second harmonic signal closely follows the phase of the applied test signal up to a finite saturation frequency (here shown as >1.0 KHz) while the conductor second harmonic signal lags 90 o at the same frequency.
  • FIG. 9 illustrates the phase detection to discriminate defect signals from conductor signals.
  • Oscillator 5 produces a low distortion sinewave signal which is buffered by amplifier 6 which provides a high current drive. This is applied through the device 3 under test. A direct current is also applied to the device 3 under test. If a constriction causing heating is encountered, a second harmonic is generated. This second harmonic generated voltage (2f o GV) appears with the driving signal and is very small compared to the drive signal. The fundamental signal V f0 is rejected by a filter 8 and the remaining signal is amplified, filtered again, and amplified. The remaining signal has a large component (2f O CV) due to resistance heating along the length of the conductor.
  • the signal is phase-sensitive-demodulated by phase detector 12 and converted to a direct current voltage. This DC voltage is filtered as required by filtering means in phase detector 12.
  • Log amplifier 17 converts to the signal so it can be recognized over 4 to 5 decades of 2f O GV strength.
  • a synchronous signal from the oscillator is derived from frequency doubler 14, 2f 0 band pass filter 15 and phase shifter 16.
  • a continuity detector 21 and continuity indicator 22 are used.
  • Threshold detector 19 and defect indicator 20 are also for ease of use. Both these indicators are placed so that an operator can easily find defects. When continuity is not made between the probes to the device under test, the linear signal amplifier is disabled so false readings are not made.
  • the tester is calibrated for maximum detection of a detector phase to be selected from a range centered slightly above zero (0) degrees out of phase with the AC component of the test signal so as to maximize discrimination between the zero (0) degrees phase of the defect second harmonic signals and the near 90 degrees phase of the good conductor signals. See Fig. 8.
  • Calibration may be done by using as a standard a circuit with known defects or as a standard a circuit known to be defect free.
  • FIG. 10 is a graph illustrating some of the properties of copper.
  • the unit of the abscissa is the mil (0.0254 mm); the unit of the ordinate is frequency in hertz. As can be seen the cutoff frequency tends to increase as a function of decreasing length of the defect. Calibration may be optimized by the operator by selection of a frequency appropriate to the type of defect suspected.
  • Frequency F (HZ) is the test frequency; the line shows the frequency at which there is 3DB rolloff, where the response is down by a factor of two.
  • FIG. 11 is a theoretical graph of nonlinear conductivity of copper as a function of defect resistance.
  • the nonlinear conductivity (NLC) tends to increase as the resistivity of the defect (RD) increases.
  • FIG. 12 is a theoretical explanation of graphical form.
  • Fig. 12 relates the length and area of a hypothetical defect in copper with the predicted second harmonic generation. Abscissa numbers are in units of (mil) 2. The brdinate numbers are in mils and it is to be noted that the numbers on a log scale. The constriction lengths and constriction areas are related to those shown in Fig. 4 as length D and area A .
  • Figure 12 shows that there are ranges of defects which may be tested for; these defects have differing second harmonic voltage levels. Certain metallurgies may tend to have larger defects, or lower conductivity, than other metallurgies and thus the tester may require differing calibration. The lines on the graph are in microvolts per ampere (peak) cubed i.e. ⁇ V/Ap 3 . This graph shows that the second harmonic signals from the defect become very small as the defect detection requirement becomes more stringent. Tiny defects produce tiny singals, which continue to be obscured by large signals from the good conductors.
  • the foregoing apparatus is frequently able to detect incipient or intermittent faults in circuit patterns, which faults are not detectable through ordinary testing techniques.

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EP83102551A 1982-04-30 1983-03-15 Dispositif et méthode pour tester les propriétés conductrices d'un conducteur Expired EP0094486B1 (fr)

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Application Number Priority Date Filing Date Title
US06/373,318 US4496900A (en) 1982-04-30 1982-04-30 Nonlinearity detection using fault-generated second harmonic
US373318 1989-06-29

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EP0094486A1 true EP0094486A1 (fr) 1983-11-23
EP0094486B1 EP0094486B1 (fr) 1985-09-11

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1988001390A1 (fr) * 1986-08-13 1988-02-25 Villamosenergiaipari Kutató Intézet Dispositif de mesure de la resistance de contact et aiguille de mesure a utiliser avec le dispositif
EP0301631A2 (fr) * 1987-07-20 1989-02-01 The Bentley-Harris Manufacturing Co. Article composite tressé
EP0301631A3 (fr) * 1987-07-20 1991-01-30 The Bentley-Harris Manufacturing Co. Article composite tressé
EP0372168A2 (fr) * 1988-12-02 1990-06-13 International Business Machines Corporation Détection de défaut utilisant des signaux d'intermodulation
EP0372168A3 (fr) * 1988-12-02 1991-05-29 International Business Machines Corporation Détection de défaut utilisant des signaux d'intermodulation
WO1997001102A1 (fr) * 1995-06-22 1997-01-09 Genrad, Inc. Systeme de detection d'anomalies dans les connexions entre circuits integres et rubans de circuits imprimes
US5736862A (en) * 1995-06-22 1998-04-07 Genrad, Inc. System for detecting faults in connections between integrated circuits and circuit board traces
GB2367631A (en) * 2000-08-09 2002-04-10 Rolls Royce Plc Device and method for fatigue testing a specimen
US6732591B2 (en) 2000-08-09 2004-05-11 Rolls-Royce Plc Device and method for fatigue testing of materials
GB2367631B (en) * 2000-08-09 2004-12-22 Rolls Royce Plc A device and method for fatigue testing of materials
GB2482053A (en) * 2010-07-12 2012-01-18 Vivax Metrotech Corp Fault locator with compensation for phase creepage
GB2482053B (en) * 2010-07-12 2014-03-12 Vivax Metrotech Corp Fault Locator

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DE3360758D1 (en) 1985-10-17
EP0094486B1 (fr) 1985-09-11
JPS58191973A (ja) 1983-11-09
US4496900A (en) 1985-01-29
JPH0317109B2 (fr) 1991-03-07

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